Superhard dielectric compounds and methods of preparation

ABSTRACT

Novel superhard dielectric compounds useful as gate dielectrics in microelectronic devices have been discovered. Low temperature methods for making thin films of the compounds on substrate silicon are provided. The methods comprise the step of contacting a precursor having the formula H 3 X—O—XH 3 , wherein X is silicon or carbon with a compound comprising boron or nitrogen In a chemical vapor deposition (CVD) chamber or with one or more atomic elements in a molecular beam epitaxial deposition (MBE) chamber. These thin film constructs are useful as components of microelectronic devices, and specifically as gate dielectrics in CMOS devices.

CROSS REFERENCE

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/328,967 filed Oct. 11, 2001, the disclosure ofwhich is incorporated by reference herein in its entirety.

STATEMENT OF GOVERNMENT FUNDING

The U.S. Government through the US, Army Research Office providedfinancial assistance for this project under Grant No. DAAD19-00-1-0471and through the National Science Foundation under Grant No. DMR-9986271,Grant No. DMR 9902417 and Grant No. ECS 0000121. Therefore, the UnitedStates Government may own certain rights to this invention.

FIELD OF INVENTION

This invention relates generally to certain super-hard dielectriccompounds useful as gate dielectrics in microelectronic devices. Lowtemperature methods for depositing thin films of these compounds ontosilicon substrates are presented.

BACKGROUND

Recently, the challenge of creating smaller dimensions inmicroelectronic devices has demanded the use of new materials for thegate dielectric—either thinner silicon oxide layers or new compoundshaving a higher dielectric constant.

Silicon dioxide (SiO₂) is a classical refractory material and the mostcommon gate dielectric in microelectronic devices. Its structure is madeup of SiO₂ tetrahedra in which each oxygen forms two bonds withneighboring Si atoms ((SiO4)⁻⁴ tetrahedra connected through bridgingoxygens). The performance of SiO₂-containing devices is limited bydopant diffusion out of poly-Si and direct tunneling through SiO₂, andwhen off-state, power dissipation becomes comparable to active power.

Current efforts are focused on replacing SiO₂ with nitride (Si₃N₄) oroxynitride (SiOxNy) films with K ˜5-7.5 [1-6] or with alternative higherK (˜20-30) films [7,8]. In recent years, nitride oxides (siliconoxynitrides) have been widely investigated as possible substitutes forSiO₂ because of their higher stability and durability, their ability toprevent boron diffusion, and their higher dielectric constant. Theintroduction of three-coordinate nitrogen into SiO₂ increases thecross-linking in the structure, resulting in a compound having higherdensity, strength, and hardness in comparison to the pure silicon oxide.Compounds in the Si—O—N system exhibit good thermal, chemical, andmechanical stability, as well as diffusive barrier and dielectricproperties [9]. In addition, Si₂N₂O has superior oxidation resistanceand thermal shock resistance compared to Si₃N₄. Most of the reportedSi—O—N systems are amorphous and appear to have a higher dielectricconstant than the pure oxide.

However, crystalline materials with well-defined compositions andstructures have been sought which will give significant improvements inmechanical and electrical properties over more amorphous forms of thesecompounds. The synthesis of phases with well-defined composition andstructure is desirable because it may lead to significant improvementsand/or controllability in the mechanical, electrical, and dielectricproperties [10,11].

One such phase is stoichiometric, silicon oxynitride (Si₂N₂O), arefractory material having all the aforementioned and desirableproperties. Si₂N₂O has the high-pressure B₂O₃ structure [12] and iscomposed of SiN₃O tetrahedral, corner-linked by O and N atoms. Thisstructure is illustrated in FIG. 2. In this structure, the oxygenbridges two Si (as in SiO₂) and the N and Si atoms are, respectively, inthree and four fold coordination as in Si₃N_(4 [)13].

The synthesis of this compound and the search for related silicon-baseddielectric materials has been the focus of intense research because oftheir potential for enhanced performance compared to SiO₂ and Si₃N₄based devices [14,15]. However, despite their attractive properties, asuitable synthesis technique for silicon oxynitrides and relateddielectrics at relatively low processing temperatures, as required insilicon device technology, is still lacking.

IN THE DRAWINGS

FIG. 1 is a ball-and-stick model illustrating the unit cell structure ofSi₂B₂O.

FIG. 2 is a ball-and-stick model illustrating the structure of Si₂N₂O.

FIG. 3 is a Rutherford Back Scattering (RBS) spectrum of a Si₂N₂O filmdeposited at 850° C. The RBS simulation by RUMP, shown as a dashed line,gives the atomic compositions of Si, O, and N.

FIG. 4 illustrates the L_(2,3) ionization edge of Si and the Kionization edges of O and N (inset) in an EELS spectrum of Si₂N₂O.

FIG. 5 is a SIMS elemental depth profile of Si₂N₂O showing a uniformdistribution of the elements.

FIG. 6 is a FTIR spectrum of a Si₂N₂O showing the N—Si—O absorptionpeaks corresponding to stretching (900 cm⁻¹) and bending (470 cm⁻¹)modes.

FIG. 7 is AFM image of the Si2B2O film surface showing relatively flatmorphology and an array of indentations used to determine themicrohardness. Inset is an enlarged view of typical nanoindentation.

SUMMARY

Novel superhard dielectric compounds useful as gate dielectrics inmicroelectronic devices have been discovered. Low temperature methodsfor making thin films of the compounds on substrate silicon areprovided. The methods comprise the step of contacting a precursor havingthe formula H₃X—O—XH₃, wherein X is silicon or carbon with a compoundcomprising boron or nitrogen in a chemical vapor deposition (CVD)chamber or with one or more atomic elements in a molecular beamepitaxial deposition (MBE) chamber. These thin film constructs areuseful as components of microelectronic devices, and specifically asgate dielectrics in CMOS devices.

Compounds having a formulae XqYpZtO wherein X is silicon or carbon, Y isboron or nitrogen, Z is gallium or aluminum, O is oxygen and q and p areeach an integer having a value of 1, 2 or 3 and t is zero or 1, providedthat when X is silicon, and t is zero, Y is not nitrogen are presented.Also presented are non-stoichiometric compounds having the formulaeXqYpZtO wherein X is silicon or carbon, Y is boron or nitrogen, Z isgallium or aluminum, O is oxygen wherein one or more of the values of q,p or t are non-integral.

In certain preferred embodiments of the invention the compounds have adielectric constant between 3 and 7, most preferably between about 5.5and 6.6.

In certain other preferred embodiments the compounds have a hardness ofbetween about 17 to 25 GPa.

In one preferred embodiment of the present invention X is Si and Y isboron and most preferably have the formula Si₂B₂O or SiB₂O.

In other preferred embodiments of the present invention, X is carbon andY is boron and most preferably has the formula C₂B2O.

In other preferred embodiments X is silicon, Y is nitrogen and Z isaluminum, most preferably the compound having the formula Si₂N₃AlO.

Most preferably the non-stoichiometric compounds of the presentinvention are silicoxynitrides wherein X is silicon, Y is nitrogen andthe values of q, p and t are non-integral.

In an important aspect of the present invention, the compounds areprovided as thin films deposited on a silicon substrate. Preferably thinfilms of the compounds of the present invention have a thickness ofbetween about 5 and 500 rim. Most preferably the silicon substrate, asilicon wafer, e.g., is Si(100), Si(111) or doped Si(111) as generallyutilized as semiconductor devices. In certain preferred embodiments, thesilicon substrate comprises a native oxide layer. In other preferredembodiments, the silicon substrate is cleaned prior to deposition offilm. In yet other preferred embodiments the silicon substrate comprisescompliant buffer layers. Substrates other than silicon generallyemployed in semiconductor devices may likewise be utilized.

In an important aspect of the present invention, microelectronic devicescomprising the present thin film of any of the compounds of the presentinvention deposited on a suitable substrate are provided. Because oftheir dielectric and other physical properties, thin films of thecompounds of the present invention are useful gate dielectrics inmicroelectronic devices CMOS, e.g., and may be incorporated intosemiconductor devices generally as substrates for other components ofintegrated circuits by methods known in the art.

In another important aspect of the invention, low temperature methodsfor preparing thin film of the present superhard dielectric compoundsare provided. These low-temperature methods are compatible with currentsilicon processing technologies. Methods are provided for preparing thinfilms of compounds having a formulae XqYpZtO wherein X is silicon orcarbon, Y is boron or nitrogen, Z is gallium or aluminum, O is oxygenand q and p are each an integer having a value of 1, 2 or 3 and t iszero or 1 comprising the step of contacting precursor having the formulaH₃X—O—XH₃ with a reactive species containing Y or Z in the presence ofsubstrate under conditions whereby thin film of the compound isdeposited on the substrate. Methods are provided for contacting theprecursor and reactive species in a chemical vapor deposition (CVD)chamber or a molecular beam epitaxial (MBE) chamber. The thin filmsprepared by the methods generally have a thickness between about 5 and500 run. Preferably, the substrate is Si(100), Si(111) or doped Si(111).Other substrates known to the art and used as substrate in preparationof thin film devices may also be employed. In certain preferredembodiments of the invention, the substrate comprises a native oxidelayer. In certain other preferred embodiments, the substrate is cleanedprior to deposition of thin film compounds. In yet other preferredembodiments the substrate may comprise a compliant buffer layer.

In certain preferred embodiments of the method of the present invention,methods are presented for preparing a compound having the formula XqYpOwherein X is silicon, Y is boron, O is oxygen and q and p are each aninteger having a value of 1 or 2, comprising the step of contacting aprecursor having the formula H₃X—O—XH₃ with a reactive compound havingthe formula (YL₃)_(v) wherein L is hydrogen or halide and v is 1 or 2 inthe presence of substrate in a chemical vapor deposition chamber underconditions whereby thin film of said compound is deposited on saidsubstrate. Thin films made by this preferred method are presented.Microelectronic devices comprising the deposited thin films arepresented.

In a preferred embodiment of this method, low temperature methods fordepositing superhard dielectric thin films of Si₂B₂O on a siliconsubstrate are presented. In these embodiments, essentially equimolaramounts of precursor H₃SiOSiH₃ and (BH₃)₂ are contacted in a CVD chamberat a temperature at about 700° C. to 1000° C., most preferably about700° C., in the presence of the silicon substrate under conditionswhereby the H₃SiOSiH₃ and B₂H₆ react to form thin film of Si₂B₂O on thesilicon substrate. In these preferred embodiments, films of Si₂B₂Ohaving a thickness of about 5 to 500 nm may be formed on siliconsubstrate, Si(100) or Si(111) or doped Si(111), for example. Thesubstrate may comprise a native oxide layer, or may be cleaned beforethe deposition of film. Thin film of Si₂B₂O on a silicon substrate thinfilm of Si₂B₂O are provided.

In another preferred embodiment, low temperature methods for depositingsuperhard dielectric thin films of SiB₂O on a silicon substrate arepresented. In these embodiments, equimolar amounts of precursorH₃SiOSiH₃ and (BH₃)₂ are contacted in a CVD chamber at a temperaturebetween about 500-650° C. in the presence of the silicon substrate underconditions whereby the H₃SiOSiH₃ and B₂H₆ react to form thin film ofSi₂B₂O on the silicon substrate. In these preferred embodiments, filmsof SiB₂O having a thickness of about 5 to 500 nm may be formed onsilicon substrate, Si(100) or Si(111) or doped Si(111), for example. Thesubstrate may comprise a native oxide layer or may be cleaned before thedeposition of film 34. Thin film of SiB₂O on a silicon substrate isprovided.

In an important aspect of the invention, microelectronic devicescomprising thin film of silicoxyborides, most specifically SiB₂O orSi₂B₂O are given.

In yet another preferred embodiment, low temperature methods fordepositing superhard dielectric thin films of Si₂N₂O on a siliconsubstrate are presented. In these preferred embodiments, essentiallyequimolar amounts of precursor H₃SiOSiH₃ and NH₃ are contacted in a CVDchamber at a temperature between about 650° C. to 850° C. in thepresence of the silicon substrate under conditions whereby the H₃SiOSiH₃and NH₃ react to form thin film of Si₂N₂O on the silicon substrate. Inthis preferred method, thin film of Si₂N₂O having a thickness of about 5to 500 nm may be formed on a silicon substrate, Si(100) or Si(111) ordoped Si(111), for example. The substrate may comprise a native oxidelayer or may be cleaned prior to deposition of film. Thin film of Si₂N₂Oon a silicon substrate prepared by these methods are given.

In another important aspect of the invention microelectronic devicescomprising thin film of Si₂N₂O made by the methods of the presentinvention are presented.

In yet another preferred embodiment of the present invention, methodsfor depositing superhard thin films of B₂C₂₀ on a silicon substrate arepresented. In these preferred methods, essentially equimolar amounts ofH₃COCH₃ and BCl₃ are contacted in said chamber at a temperature betweenabout 650° C. to 850° C. in the presence of the silicon substrate underconditions whereby the H₃COCH₃ and BCl₃ react to form thin film of B2C20on the silicon substrate. B2C20 films formed by these methods may have athickness of about 5 to 500 nm. The substrate is preferably silicon,Si(100) or Si(111) or doped Si(111), for example. The substrate maycomprise a native oxide layer or may be cleaned prior to deposition offilm. Thin film of B₂C₂₀ on silicon substrate are provided.

In yet another important aspect of the invention, microelectronicdevices comprising thin film of borocarboxyoxides, specifically thinfilm B₂C₂₀ are given.

In another preferred embodiment of the method of the present invention,methods are presented for preparing thin film of a compound of thepresent invention having a formula XqYpZtO wherein X is silicon orcarbon, Y is boron or nitrogen, Z is gallium or aluminum, O is oxygenand q and p are each an integer having a value of 1, 2 or 3 and t iszero or 1 and for preparing non-stoichiometric compounds XqYpZtO whereinone or more of the values of q, p or t are non-integral. The methodcomprises the step of directing Y atoms at a precursor having theformula H₃X—O—XH₃ in a molecular beam epitaxial chamber in the presenceof a silicon substrate under conditions whereby the precursor and Yatoms combine to form thin film on the substrate. Preferably thesubstrate is Si(100), Si(111) or doped Si(111) and may comprise a nativeoxide layer or be cleaned by methods known in the art prior todeposition. Thin film of these compounds on a silicon substrate areprovided. Substrates other than silicon known to the art may also beemployed as substrate.

In another important aspect of the invention, microelectronic devicescomprising thin film of a compound made by these methods are provided.

In preferred embodiments of the method of this present invention,superhard thin films of non-stoichiometric siliconoxynitrides areprepared. In this preferred method, atomic nitrogen generated in amolecular beam deposition chamber is directed at precursor H₃SiOSiH₃ inthe presence of silicon substrate under conditions whereby the precursorand nitrogen atoms react to form thin film of non-stoichiometric siliconoxynitrides on the silicon substrate. Preferably the temperature of thechamber is about 850° C. to 950° C. The substrate may be Si(100),Si(111), doped Si(111) or other substrate known to the art and maycomprise a native oxide layer, compliant buffer or may be cleaned priorto deposition of the thin film. Preferably the temperature of saidchamber is between about 850 to 950° C. and the substrates is highlydoped Si(111). Thin film of non-stoichiometric silicoxynitridesdeposited on a silicon substrate by these methods are provided.

In yet another important aspect of the invention, microelectronicdevices comprising a thin film of non-stoichiometric silicoxynitridemade by the present methods are provided.

In certain preferred instances of the invention, methods for depositingsuperhard thin films of Si₂N₃AlO on a silicon substrate are given. Inthese methods atomic nitrogen and atomic aluminum are directed atprecursor is H₃SiOSiH₃ in a molecular beam deposition chamber in thepresence of a silicon substrate under conditions whereby the disiloxanereacts with nitrogen atoms and aluminum atoms to form thin film ofSi₂N₃AlO on the silicon substrate. In these instances, the siliconsubstrate may comprise compliant buffer layers comprising in situgenerated SiAlONS and related Al silicon oxynitrides. Thin film ofSi₂N₃AlO on a silicon substrate are provided.

In yet another important aspect of the present invention,microelectronic devices comprising thin film of Si₂N₃AlO are provided.

In an important aspect of the invention, compounds having the formulaH₃XOXH₃ wherein X is silicon or carbon are presented as precursors inthe preparation of the compounds of the present invention. In preferredinstances, H₃SiOSiH₃ is presented as a precursor in the preparation ofthe compounds of the silicon-based compounds of the present invention.In other preferred instances, H₃COCH₃ is presented as a precursor in thepreparation of the compounds of the carbon-based compounds of thepresent invention.

In an important aspect of the present invention, methods are providedfor preparing disiloxane having the formula H₃SiOSiH₃. The methodcomprises the steps of contacting a halosiloxane, preferablyCl₃SiOSiCl₃, with a salt of gallium tetrahydride, preferably LiGaH₄, andcapturing gaseous H₃SiOSiH₃ generated during the reaction betweenhalosiloxane and the hydride. Disiloxane prepared by this method may beused as a precursor for the preparation of thin films of the compoundsof the present invention. Preferred compounds made from siloxaneprepared by the method of the present invention are Si₂N₂O,non-stoichiometric siloxynitrides, silicoborohydrides, most preferablySiB₂O and Si₂B₂O, and Si₂N₃AlO.

In yet another aspect of the compounds of the present invention may beused as superhard coatings in a variety of applications.

DETAILS OF THE INVENTION

While the present invention will be described more fully hereinafterwith reference to the examples and accompanying drawings, in whichaspects of the preferred manner of practicing the present invention areshown, it is to be understood at the outset of the description whichfollows that persons of skill in the appropriate arts may modify theinvention herein described while still achieving the favorable resultsof this invention. Accordingly, the description which follows is to beunderstood as being a broad, teaching disclosure directed to persons ofskill in the appropriate arts, and not as limiting upon the presentinvention.

This invention provides novel superhard compounds having dielectricconstants that make them useful as gate dielectrics in CMOS devices andas superhard coatings in a variety of applications. In certain preferredinstances, the compounds comprise a Si—O backbone structure and a lightelement boron or nitrogen. In other instances the compounds comprise aC—O backbone structure and a light element, boron or nitrogen. Compoundshaving the Si—O backbone and nitrogen and aluminum are also provided.

Generally, the crystalline structures of these compounds are compactwhich gives them their hardness and electronic properties. Preferredcompounds Si₂B₂O and SiB₂O, for example, are isoelectronic to carbon(i.e., four valence electrons per atom) and they crystallize with highlydense diamond-like structures in which all the constituent elements aretetrahedrally coordinated. This leads to superior properties such assuperhardness and high stability at extreme conditions. In fact, suchmaterials may be alternatives to diamond in high performanceapplications. Si₂B₂O has a structure that consists of SiB₂O tetrahedralinked at their corners by O and B atoms. This is essentially the Si₂N₂Ostructure with all the N atoms at the trigonal sites replaced by sp²hybridized B (FIG. 1). Alternate structure related to diamond that isdenser and harder may also be possible. In this structure all theelements occupy exclusively tetrahedral sites as in diamond. Thisstructure is feasible since SiB₂O is isoelectronic to diamond and is inessence a stoichiometric hybrid between Si and B₂O. The latter is ahighly sought binary phase of boron with 3-D diamond-like structure thathas been predicted to have extreme hardness and other importantelectronic and mechanical properties.

C₂B₂O is the carbon analogue of Si₂B₂O. This system is a stoichiometrichybrid between diamond and the superhard phase B₂O phase. C₂B₂O in thediamond cubic structure but has superior properties such assuperhardness as well as higher resistance to oxidation and higherthermal stability than diamond. Si₂N₂O another preferred embodiment hasthe high pressure B₂O₃ structure and it is composed of SiN₃O tetrahedralinked at their corners by O and N atoms (FIG. 2). Each oxygen isconnected to two Si (as in SiO₂) and the N and Si atoms are,respectively, three and four fold coordinate as in Si₃N₄.

Certain preferred compounds of the present invention are silicon-basedoxygen and boron-containing compounds having the formulaSi_(a)B_(b)O_(d), Most preferably Si₂B₂O or SiB₂O. Other preferredcompounds are, non-stoichiometric silicon-based oxygen andnitrogen-containing compounds, siliconoxynitrides having the formulaSi_(a)N_(b)O. In yet other preferred embodiments carbon-based compoundshaving the formula C_(a)B_(b)O, most preferably C₂B₂O are provided. Incertain other preferred embodiments of the present invention, compoundshaving the formula Si_(a)N_(b)Z_(c)O_(d) wherein Z is aluminum isprovided. Most preferably the compound has the formula Si₂N₃AlO.

A highly practical and a low-temperature chemical vapor deposition (CVD)method, involving an entirely new approach based on a stoichiometricheterogeneous reaction from gaseous reactants, is described fordepositing Si₂N₂O films (5-500 nm) on Si substrates. A new and practicalmethod for depositing superhard thin films of refractory and dielectricsilicon oxynitrides, via CVD and MBE reactions of the molecularprecursor H₃Si—O—SiH₃, is demonstrated. Specifically, stoichiometricSi₂N₂O and non-stoichiometric SiO_(x)N_(y) films were deposited on Sisubstrates at 600-850° C., and characterized for their phase,composition, and structure by RBS, EELS, FTIR, FESEM, and HRTEM. Theleakage current density voltage J_(L)-V) characteristics and thecapacitance-voltage (C-V) as a function of frequency were determined onMOS (Al/Si₂N₂O/SiO/p-Si) structures. The leakage current density, J_(L)at −6V (+6V) for a 20 nm Si₂N₂O film was 0.1 nA/cm² (0.05nA/CM²). Thedielectric permittivity, K, estimated from the capacitance density inaccumulation, was 6 and frequency dispersionless. From the negative flatban shift (ΔV_(fb)) of 150 mV, the positive fixed charge density (N_(f))at the Si(100)/SiO interface was calculated to be 2.3×10¹¹/CM³. Themicrohardness of Si₂N₂O was determined to be 18 GPa.

The key aspect of this deposition technique is the use of a completelyinorganic source (H₃Si—O—SiH₃) that incorporates the crucial Si—O—Sibuilding block of the target solids, and which does not possess thetypical impurity elements such as Cl and C that are potentiallydetrimental to the electrical and dielectric properties of the material.Moreover, its stoichiometric reaction with NH₃ leads to the completeelimination of its H ligands to yield high purity Si—O—N films. Thisprecursor compound also offers an ideal synthetic route for theformation of technologically important oxynitrides, with controlledstoichiometries, and at low temperatures compatible with siliconprocessing technology.

A novel low-temperature (600-850° C.) chemical vapor deposition (CVD)method, involving the reaction between disiloxane (H₃Si—O—SiH₃) andammonia (NH₃) is presented to deposit stoichiometric, Si₂N₂O, andnon-stoichiometric, SiO_(x)N_(y), silicon oxynitride films (5-500 nm) onSi substrates. The gaseous reactants are free from carbon and otherundesirable contaminants. The deposition of Si₂N₂O on Si [with (100)orientation and a native oxide layer of 1 nm] was conducted at apressure of 2 Torr and at extremely high rates of 20-30 nm per minutewith complete hydrogen elimination.

The deposition rate of SiO_(x)N_(y) on highly-doped Si [with (111)orientation but without native oxide] at 10⁻⁵ Torr was 1.5 nm perminute, and achieved via the reaction of disiloxane with N atoms,generated by an RF source in an MBE chamber. The phase, composition andstructure of the oxynitride films were characterized by a variety ofanalytical techniques. The hardness of Si₂N₂O, and thecapacitance-voltage (C-V) as a function of frequency and leakage currentdensity-voltage (J_(L)-V) characteristics were determined on MOS(Al/Si₂N₂O/SiO/p-Si) structures. The hardness, frequency-dispersionlessdielectric permittivity (K), and J_(L) at 6V for a 20 nm Si₂N₂O filmwere determined to be 18 GPa, 6, and 0.05-0.1 nA/cm³, respectively.

Additionally, the deposition of non-stoichiometric SiO_(x)N_(y) is alsodemonstrated. The films are characterized by Rutherford backscatteringspectroscopy (RBS), secondary ion mass spectrometry (SIMS),high-resolution transmission electron microscopy (HRTEM) andspatially-resolved electron energy loss spectroscopy (EELS), Fouriertransform infrared spectroscopy (FTIR), field-emission scanning electronmicroscopy (FESEM), a Triboscope attached to an atomic force microscope(AFM) for hardness, and electrical and dielectric methods.

The synthetic reaction is similar to that for Si₂N₂O and is illustratedby the equation (1):

H₃SiOSiH₃+B₂H₆→H₂+Si₂B₂O  (1)

Also presented are methods for preparing the carbon analogs of thesilicon-based compounds utilizing the precursor dimethyl ether, H₃COCH₃in the CVD or MBE chamber. Compounds made by these methods are, forexample, C₂B₂O.

The thin films are characterized by Rutherford backscatteringspectroscopy (RBS), secondary ion mass spectrometry (SIMS),high-resolution transmission electron microscopy (HRTEM) andspatially-resolved electron energy loss spectroscopy (EELS), Fouriertransform infrared spectroscopy (FTIR), field-emission scanning electronmicroscopy (FESEM), a Triboscope attached to an atomic force microscope(AFM) for hardness, and electrical and dielectric methods.

Determination of the hardness of the compounds give values of GPa ofbetween about 17 to 25 Gpa. These values illustrate the usefulness ofthe compounds as superhard coatings in a variety of applications. FIG. 7is AFM image of the preferred embodiment Si2B20 film surface showingrelatively flat morphology and an array of indentations used todetermine the microhardness. Inset is an enlarged view of typicalnanoindentation.

Chemical Precursors Disiloxane

The key feature in the method for deposition of thin films of thepresent invention comprising silicon is the use of the simple disiloxane(H₃Si—O—SiH₃) precursor [16]. The major advantage of utilizingH₃Si—O—SiH₃ is the presence of the Si—O—Si framework in the molecule,which provides both the building block for the desired 3-D network andessentially fixes the necessary Si to 0 ratio. Additionally, theH₃Si—O—SiH₃ compound is stable and volatile with a boiling point of −15°C. The vapor pressure at −82° C., 145° C. and −23° C. are 15, 195 and563 Torr, respectively [16]. The precursor can be stored almostindefinitely in stainless steel containers and like most silanes,ignites spontaneously but not explosively upon contact with air.Moreover, it does not contain carbon or any other potentially impureelements (e.g., Cl, F) in the molecular structure. The deposition ofSi₂N₂O films is illustrated in the following reaction (2):

H₃Si—O—SiH₃+NH₃→6H₂+Si₂N₂O  (2)

Moreover, the use of active N species in place of NH₃, with controlledenergies, may also be used to tailor the N to 0 ratio in a desiredmaterial. Therefore, nonstoichiometric films (SiO_(x)N_(y)), withcomposition and property intermediate to those of stoichiometric Si₃N₄and stoichiometric SiO₂, may be readily engineered. Disiloxane iscommercially available and also may be prepared by methods disclosed inthe present invention.

Dimethyl Ether

The deposition of thin films of the present invention comprising carbonproceeds through the use of the dimethyl ether precursor. Dimethyl etheris commercially available. The simple dimethyl ether precursor may beused in either the CVD chamber or the MBE chamber to make the carbonanalogues of the compounds of the present invention. Carbon analogues ofthe silicon compounds have similar hardness and dielectric properties.

The deposition of B₂C₂₀ films is illustrated in the following reaction(3):

H₃C—O—CH₃+BCl₃→B₂C₂O+6HCl  (3)

EXPERIMENTAL SECTION Example 1

This example illustrates the deposition of Si₂N₂O films on siliconsubstrate in a chemical vapor deposition (CVD) chamber using siloxane asprecursor.

The deposition of Si₂N₂O films was carried out in a CVD reactorconsisting of a cold-wall quartz tube fitted with a recirculatingjacket. The reactor wall temperature was maintained at 700° C. byrecirculating preheated ethylene glycol. The Si substrate was p-Si waferhaving resistivity of 4.5×10-3 ohm/cm. The substrates were inductivelyheated using a high-grade, single-wafer graphite susceptor. Prior to itsinitial use, the susceptor was out-gassed at 1100° C. under high vacuum(10⁻³ Torr), and then coated with Si via SiH₄ decomposition. The pumpingsystem was comprised of a high capacity turbo-molecular pump and acorrosion-resistant pump. The former was used to obtain high vacuumbefore and after each deposition, and the latter was used duringdeposition. A typical reactor base pressure was 5-6×10⁻⁷ Torr. Thegaseous reactants, H₃Si—O—SiH₃ and NH₃, were diluted with research gradeN₂ and introduced into the reactor through precalibrated mass flowcontrollers. The deposition was conducted at a pressure of 2 Torr andtemperatures between 600-850° C. Under these conditions, stoichiometricSi₂N₂O films ranging in thickness between 5 and 500 run, were depositedon Si [with an orientation of (100) and a native oxide layer of 1 nm] atextremely high rates of 20-30 nm per minute.

Physico-Chemical Characterization of Si₂N₂O Films Prepared in Example 1

RBS in the random mode was routinely used to obtain the Si, N, and Oconcentration and to estimate the film thickness. A typical plot isillustrated in FIG. 2. Additionally, elastic N and O resonance nuclearreactions at 3.72 MeV and 3.0 MeV, respectively, were used to establishthe precise Si₂N₂O elemental ratios. Since forward recoil experimentsindicated that the hydrogen content was at background levels, theelimination of the Si—H and N—H bonds from the reactants occurredcompletely during growth.

SIMS was used to confirm the presence of the desired elements and theabsence of carbon impurities, and to demonstrate that the elementalcontent was homogeneous throughout the material. A representative SIMSdepth profile, showing the highly uniform elemental distribution in thefilm thickness direction, is given in FIG. 5.

HRTEM (not shown here) indicated that the films were highly uniform inthickness and displayed flat and smooth surface morphology. The selectedarea electron diffraction (SAED) and high-resolution images confirmedthat the material was amorphous. Spatially-resolved EELS, used toexamine the elemental content at the nanometer scale and characterizethe local bonding environment of the atoms, showed that the constituentelements appeared at every nanometer step probed; this consistent with asingle-phase material. The absolute elemental concentration (determinedby EELS) was close to the stoichiometric value for Si₂N₂O, whichcorroborated the RBS results. An EELS spectrum featuring the ionizationedges of the elements is shown in FIG. 4. The near-edge fine structureis indicative oa a 3-D Si₂N₂O network.

The FITR spectrum in FIG. 6 exhibited phonon modes consistent with thesingle-phase Si₂N₂O. A strong, well-defined peak centered at 900 cm⁻¹and a weak peak at 470 cm-I corresponds to the N—Si—O stretching andbending modes, respectively, of the Si₂N₂O phase [15]. Note, the 900cm⁻¹ peak is located at frequencies intermediate to those of thecorresponding stretching odes for stoichiometric SiO₂ (˜980 cm⁻¹) andSi₃N₄ (˜850 cm-1). Moreover, in the region between 2100 cm-1 and 2000cm-1, of the spectrum, additional peaks attributable to Si—H vibrationsare absent. This is consistent with the RBS result of completeelimination of H ligands from the precursor.

The hardness of the films was determined using a Hysitron Triboscopeattached to a Nanoscope III AFM (digital instruments). The hardness isdefined as the applied load divided by the surface area of theimpression when a pyramidal shaped diamond indentor is pressed normallyinto the film. Pure quartz (SiO₂) was used as a standard and itshardness was measured to be close to 9.5 GPa. For example, the hardnessof single-crystal Al2O3 (sapphire) was measured to be 22 GPa. Using thesame experimental conditions, the hardness of the Si₂N₂O films are wasapproximately 18 GPa.

Characterization of Electrical and Dielectric Properties of Si₂N₂O FilmsPrepared in Example 1.

Including tile native oxide layer (SiO₂; x˜1) of 1 nm [8], the observedSi₂N₂O film thicknesses by FESEM were 20 nm, 30 nm, 37.5 nm, and 65 nm,in agreement with RBS and HRTEM results. From the four-point probemeasurement of the electrical resistivity of the Si wafer, the dopantdensity was estimated to be 2.5×10¹⁹ cm^(−3 [)16]. For the roomtemperature electrical and dielectric measurements, aluminum (Al) topelectrodes (100 nm thick and 530 um diameter) were deposited ontosamples through a shadow mask by e-beam evaporation. Also, 100 nm Alfilms were deposited on the backside of Si to improve the bottomcontacts. The samples were placed in an analytical probe system equippedwith a chuck (3190 MC Systems), and the top electrodes were contactedwith microprobes (1097 MODEL; mc Systems). The high frequency (1-100KHz, ac_(osc) 20 mV) capacitance-voltage (C-V) characteristics and thedc current-voltage (I-V) characteristics of the capacitors were measuredusing a multi-frequency LCR meter (HR Impedance analyzer, 4284A) andcurrent meter (HPn4140B), respectively.

The leakage current densities, J_(t) (with 10 s delay), at −6V (−10V)and +6 V (+10V) for a 20 nm Si₂N₂O film were 0.1 nA/cm₃ (100 nA/cm³) and0.05 nA/cm³ (3 nA/cm³), respectively. This asymmetry in the magnitude ofJ_(L) for positive and negative gate voltages stems from the asymmetryif the band alignment and band bending at the Si/SiO_(x) and Al/Si₂N₂Ointerfaces, and the consequent asymmetry in the transmission probability[19-22].

The C-V measurements were carried out on MOS (Al/Si₂N₂O/SiO/P—Si)structures. From the measured capacitance densities in accumulation(C_(acc)/A) at −5V, which were dispersionless in the frequency rangemeasured, the total equivalent SiO₂ thickness or EOT_(tot) (i.e.,EOT_(tot)−∈₀K_(SiO2)/(C_(acc)/A)) and K_(SI2N2O) as a function of Si₂N₂Othickness were calculated and are tabulated in Table I. Note, for thesecalculations the K of the interfacial SiO layer was estimated to be 7.8(assuming a linear extrapolation between the K of 11.7 for Si and 3.9for SiO₂) and quantum corrections were not applied.

From the slope of a Schotzky plot (I/C2 versus V), with data from thedepletion region (+I to +5V) of the C-V curve for a 20 nm film at 100KHz, the dopant density was calculated using the following equation [19](4):

$\begin{matrix}{N_{A} = {\frac{2}{{qK}_{s}A^{2}{{d( {1/C^{2}} )}/{dV}}} = {2.8 \times 10^{19}\mspace{11mu} {cm}^{- 3}}}} & (4)\end{matrix}$

where K.=11.7, A=0.0022 cm² and (1/C²)/dV=9.7×10¹⁶. Note, this value ofNA is in agreement with that derived from the four-point probe method.

Considering this doping level (2.8×10¹⁹/cm of p-Si, the work function ofAl (4.2 eV), and the electron affinity of Si (4.05 eV), the ideal flatband, V_(fbo)=Φ_(MS) was calculated to be −0.85 V. At 100 K·Hz, theactual V_(fb) for the Al/Si₂N₂O/SiO/P—Si structure was −1V. Thiscorresponds to a negative flat band Shift (ΔV_(fb)=V_(fb)−Φ_(MS)) of 150mV. Therefore, the positive fixed charge densityN_(f)=(ΔV_(fb)C_(acc))/qA) at the SiOSi interface was estimated to be2.3×10¹¹/cm². The potential origin of this positive charge can becorrelated with roughness at the Si(100)/SiO interface and thenon-stoichiometry of SiO_(x). [19,21,23].

Table 1 gives the measured and estimated parameters, from C-V data at afrequency of 100 KHz, for Si₂N₂O film with different thickness. Note,Φ_(MS)=−0.85 V, dopant density of p-Si is 2.8×10¹⁹/cm³, and electrodearea=0.00216 cm².

TABLE 1 Thickness of Si₂N₂O, nm t_(SiO), nm (C_(acc)/A), fF/um²EOT_(tot), nm KSi₂N₂O 20 1 2.45 14.1 5.9 37.5 1 1.29 26.7 5.7 65 1 0.843.4 6.0

Example 2

This Example illustrates the deposition of non-stoichiometric Si—O—NFilms on Si substrated prepared MBE chamber utilizing siloxane asprecursor.

The deposition of non-stoichiometric, silicon oxynitride (SiO_(x)N_(y))films, via reactions of the H₃Si—O—SiH₃ precursor with N atoms generatedby an RF source in an MBE chamber, was carried out. The base pressure ofthe chamber was 10⁻¹⁰ Torr, which increased to 10⁻⁴ Torr during thedeposition. The plasma source power was operated at 400 W with a typicalN pressure of 10⁻⁷ Torr. The SiO_(x)N_(y) films were deposited at 900°C. on highly-doped Si (111) substrates, which were previously flashed at1050° C. and 10⁻¹⁰ Torr to remove the native oxide layer. The durationof each deposition was 30 to 45 minutes, yielding an average growth rateof 1.5 nm per minute.

Characterization of Non-Stoichiometric; Si—O—N Films Made by the Methodof Example 2.

RBS analysis of these films illustrated in FIG. 3 revealed that the Si,N and O concentrations were 45 at. %, 50 at. % and 5 at. %,respectively, indicating that the oxygen content in these films weresubstantially lower than that of Si2N2O (which is 20 at. %). The FTIRspectrum showed the characteristic stretching mode at 845 cm⁻¹ which islower in energy with respect to Si₂N₂O but almost identical to that ofbeta Si₃N₄. This data indicates that the bonding arrangement of thisSiO_(x)N_(y) material is based predominately on the Si₃N₄ network withsome of the lattice sites occupied by oxygen atoms. The dramaticdeviation from tile ideal Si₂N₂O stoichiometry is attributed todisplacement of oxygen from the H₃Si—O—SiH₃ precursor by the highlyreactive N atoms. Therefore, by judicious adjustments in the growthparameters, particularly the flux of the nitrogen beam, the O content inthe films may be precisely tuned. Consequently this method provides asimple and convenient pathway leading to the formation ofnon-stoichiometric gate dielectric films with composition and propertiesintermediate to those of Si₃N₄ and SiO₂.

Example 3

This example illustrates the deposition of C₂B₂O films on siliconsubstrate in a chemical vapor deposition (CVD) chamber usingdimethylether as precursor.

The deposition of C₂B₂O films is carried out in a CVD reactor under thereaction conditions given in Example 1. The Si substrate is p-Si wafer.The gaseous reactants, CH₃—O—CH₃ and BCl₃ are diluted with researchgrade N₂ and introduced into the reactor through pre-calibrated massflow controllers. The molar ratio of BCl₃ to precursor is approximately2:1. The deposition is conducted at a pressure of 2 Torr andtemperatures between 600-850° C. Under these conditions, stoichiometricC₂B₂O films ranging in thickness between 5 and 500 run, is deposited onSi.

Example 4

This Example illustrates tile deposition of Si2B20 films on siliconsubstrate in a chemical vapor deposition (CVD) chamber using disiloxaneas precursor.

Thin films with composition close to the desired Si₂B₂O were depositedon Si(100) at 735° C. with rates ranging from 15 nm to 20 nm perminutes. An exactly stoichiometric mixture of the reactant gases and adeposition temperature above 700° C. were necessary to obtain films withSi₂B₂O stoichiometry.

Example 5

This Example illustrates the deposition of SiB₂O films on siliconsubstrate in a chemical vapor deposition (CVD) chamber using disiloxaneas precursor.

Thin films with composition close to SiB₂O were deposited on Si(100)under essentially same conditions as described in Example 4, but thetemperature was lowered to 500 to 650° C. It is proposed that the Sideficiency in this relative to the Si₂B₂O compound prepared in Example 4is due to incomplete reactions and possible elimination of SiH₄ from thethermal disproportionation of the precursor as is illustrated inEquation (4):

H₃Si—O—SiH₃+B₂H₆ H₂+SiB₂O+SiH₄  (5)

Nevertheless, the SiB₂O composition in itself is unique because it isalso isoelectronic to diamond and may crystallize with the diamondstructure.

Characterization of Si₂B₂O and SiB₂O

The elemental concentrations of Si₂B₂O and SiB₂O were determined by RBS.SIMS was also used to confirm the presence of the desired elements andthe lack of impurities, and to show that the elemental content washomogeneous through the material. FTIR showed bands corresponding toSi-0, B—O and Si—B lattice modes a result, consistent with the structureillustrated in FIG. 1. Cross-sectional TEM revealed that theas-deposited samples were amorphous. More crystalline samples may beprepared by reducing the growth rates and by conducting post-growthannealing. The hardness of Si₂B₂O was measured to be 17 GPa. Thehardness of SiB₂O was measured to be 12 GPa.

Example 6

This Example illustrates the preparation of thin film Si₂AlN₃O in a MBEchamber.

Precursor disiloxane was bombarded with nitrogen atoms and aluminumatoms in a MBE chamber under condition described in Example 2. Thehardness of Si₂AlN₃O is 25 Gpa.

Example 7

This Example illustrates the preparation of thin film B₂C₂₀ on a siliconsubstrate.

Precursor H₃COCH₃ and BCl₃ are contacted in essentially equimolaramounts in a CVD chamber according to the method described in Example 1.The chamber was maintained at a temperature of about 700° C. to 850° C.The thickness of the deposited B₂C₂₀ film was about 5 to 500 nm onSi(100) substrate. Si(III) and doped Si(111) may also be employed inthis example and said substrate may comprise a native oxide layer or becleaned by methods known in the art prior to deposition of B₂C₂O film.

Example 8

This example illustrates the preparation of disiloxane H₃SiOSiH₃.

Commercially available Cl₃SiOSiCl₃ is diluted in diethyl ether andcooled to 78° C. Solid LiGaH4 is added to the Cl₃SiOSiCl₃/solutionthrough a solid addition funnel. Gaseous O(SiH₃) is formed immediatelyand it is removed and purified by trap-to-trap distillation. The yieldis typically 30-50%. The compound is identified by mass spectrometry andIR spectroscopy and shown to be identical with commercially availabledisiloxane.

Those skilled in the art will appreciate that numerous changes andmodifications may be made to the preferred embodiments of the inventionand that such changes and modifications may be made without departingfrom the spirit of the invention. It is therefore intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

REFERENCES

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1. A compound of the formula XqYpZtO wherein X is selected from thegroup consisting of silicon or carbon, Y is selected from the groupconsisting of boron or nitrogen, Z is selected from the group consistingof gallium or aluminum, O is oxygen, wherein q and p are independently1, 2 or 3 and t is zero or 1, provided that when X is silicon, and t iszero, Y is not nitrogen.
 2. (canceled) 3-5. (canceled)
 6. The compoundof claim 1 wherein X is Si and Y is boron.
 7. The compound of claim 6having the formula Si₂B₂O.
 8. (canceled)
 9. The compound of claim 1wherein X is silicon and Y is nitrogen.
 10. The compound of claim 1wherein X is carbon and Y is boron.
 11. The compound of claim 10 havingthe formula C₂B₂O. 12-64. (canceled)
 65. The compound of claim 1 whereinat least one of p and q are 1 or
 2. 66. The compound of claim 1 whereinZ is aluminum.
 67. The compound of claim 1 wherein t is
 0. 68. Thecompound of claim 6 having the formula SiB₂O.
 69. The compound of claim1 wherein X is silicon, Y is nitrogen, and Z is aluminum.
 70. Thecompound of claim 69 having the formula Si₂N₃AlO.